A method for preparing CuCr25 contact material by using superfine powder

Abstract

The application discloses a method for preparing CuCr25 contact material by using superfine powder, and comprises the following steps: S1, raw material selection, S2, powder mixing, S3, cold isostatic pressing, S4, vacuum sintering, S5, arc melting, and S6, performance detection; the superfine chromium powder is selected, which is favorable for optimizing the volume ratio of copper-chromium powder during preparation of copper-chromium electrode rod mixed powder, that is, the superfine chromium powder and the relatively coarse copper powder are uniformly mixed in proportion, so that the maximum loose bulk density can be obtained, because the large pores between the coarse particles of the copper powder can be filled by a part of the fine particles of the chromium powder, which is favorable for the uniformity of the mixed powder and the degassing of the electrode rod during vacuum sintering, so that the electrode rod is more stable during the arc melting process, and the prepared material has more uniform and dispersed chromium phase.

Description

Technical Field

[0001] This invention relates to the field of contact material preparation technology, specifically to a method for preparing CuCr25 contact material using ultrafine powder. Background Technology

[0002] The invention of CuCr contact materials was a major breakthrough in the history of vacuum switch development. The application of CuCr contact materials has greatly improved the performance of vacuum switches, providing them with a broad prospect. The preparation process of copper-chromium contact materials is the main factor determining the physical and mechanical properties of the contact materials, and ultimately, their electrical properties. CuCr alloys belong to the segregated crystal system, making them virtually impossible to produce using traditional ingot casting processes. Currently, there are four main methods for producing CuCr alloys internationally: powder metallurgy, vacuum infiltration, vacuum casting, and arc melting. However, due to process limitations, vacuum casting and arc melting are generally chosen for preparing CuCr25 contact materials. But in vacuum casting, insufficient cooling can easily lead to segregation and dendrite formation in the contact material. Furthermore, the use of non-metallic crucibles during melting introduces foreign impurities into the alloy due to electromagnetic stirring, failing to meet market demands for high purity, low gas content, and finely dispersed chromium particles. Therefore, arc melting is increasingly favored for the preparation of CuCr25 contact materials.

[0003] The arc melting process uses water-cooled oxygen-free copper as a crystallizer to crystallize and solidify the molten material, avoiding contact with other non-metals and contaminants that could lead to inclusions in the metallographic structure. Furthermore, because the consumable electrode is dripped into the water-cooled copper crystallizer after melting, it can be rapidly cooled. The high cooling rate suppresses the segregation of Cu and Cr phases, achieving rapid crystallization and thus refining the copper-chromium crystal structure. At the same time, the combined effect of electromagnetic force and vacuum in the furnace during the arc melting process effectively reduces the inclusions and gas content in the material, purifying the alloy ingot.

[0004] The key to preparing CuCr25 contact materials lies in understanding the raw materials and equipment. Differences in powder flowability, density, and particle size during the mixing process of copper and chromium powders can lead to uneven mixing, resulting in segregation after smelting. Therefore, it is necessary to select the optimal process and parameters to produce the best contact materials at the lowest cost, meeting the needs of different users and markets.

[0005] Currently, there are still some problems in the preparation process of low-chromium CuCr25 contact materials: for example, the gas content in the material is too high, the distribution of Cr particles in the alloy microstructure is uneven and not fine enough, impurities are present, and segregation or dendrites are easily generated, which is especially unacceptable for special application fields. Based on this, this application proposes a method for preparing CuCr25 contact materials using ultrafine powder. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing CuCr25 contact material using ultrafine powder.

[0007] The technical solution of this invention is: a method for preparing CuCr25 contact material using ultrafine powder, comprising the following steps:

[0008] S1. Raw Material Selection

[0009] Weigh out high-purity, low-gas ultrafine Cr powder with a purity of 99.5%–99.9% and a particle size of 20–50 μm from aluminothermic reduction, and electrolytic Cu powder with a purity of 99.9% and a particle size of 50–80 μm from aluminothermic reduction, according to the Cr powder:Cu powder mass ratio of 23%–27%:73–77%, and set aside for later use.

[0010] S2, Powder Mixing

[0011] Electrolytic Cu powder and ultrafine Cr powder are mixed and then placed into a mixer. Stainless steel balls with a diameter of φ4-12mm are added at a ball-to-powder ratio of 1:1. The stirring speed is adjusted to 10-40 r / min and the mixing time is 2-6 h to obtain a mixture.

[0012] S3, Cold Isostatic Pressing

[0013] The rubber sleeve containing the mixture is placed in a cold isostatic press and pressed at a pressure of 150-350 MPa for a holding time of 5-10 min to obtain a consumable electrode rod.

[0014] S4, Vacuum Sintering

[0015] The consumable electrode rod was transferred to a vacuum of 1×10⁻⁶. -1 The blank is sintered in a vacuum sintering furnace of Pa, with the sintering temperature controlled between 700 and 1050°C and the holding time between 1 and 3 hours. Then it is cooled to below 60°C in the furnace to obtain the blank.

[0016] S5, electric arc melting

[0017] The sintered billet is used as a consumable electrode and transferred into a vacuum consumable arc furnace for melting. During the melting process, a protective gas is introduced. After the melting is completed, the molten liquid is poured into a water-cooled copper mold and solidified to obtain an ingot.

[0018] S6, Performance Testing

[0019] After the ingot is melted, it is cooled to 50-60°C, and then the outer diameter is rough turned, the riser and the bottom plate are sawn to remove casting defects such as shrinkage cavities. Samples are then taken for physical and chemical property testing.

[0020] Note: In this invention, the raw material for CuCr25 is selected as ultrafine chromium powder with a particle size of 20-50 μm, and the copper powder is selected as electrolytic copper powder with a particle size of 50-80 μm. For CuCr25 material, the mass fraction of chromium powder in copper-chromium powder is relatively low. Moreover, due to the large difference in melting points between copper (melting point 1083.4℃) and chromium (melting point 1857.0℃) during the smelting process, it is easy to produce copper-rich and chromium-rich materials. Selecting ultrafine chromium powder is beneficial to optimizing the volume ratio of copper-chromium powder when preparing copper-chromium electrode rods. That is, after mixing ultrafine chromium powder and coarser copper powder in a certain proportion, the maximum loose density can be obtained. This is because the large pores between the coarse copper powder particles can be filled by some of the fine chromium powder particles, which is beneficial to the uniformity of powder mixing and the degassing of the electrode rod during vacuum sintering. This ensures that the electrode rod is more stable during the arc melting process, and the chromium phase of the prepared material is more uniformly dispersed.

[0021] After melting, the molten metal is rapidly solidified using a water-cooled copper mold, providing a faster cooling rate than traditional casting methods. Because the copper mold is water-cooled, a lower temperature can be set, and the heat exchange rate is relatively high. Therefore, the CuCr alloy cools very quickly after melting, allowing the copper-chromium two-phase alloy to solidify rapidly before segregation occurs, which is beneficial for grain refinement. This further enhances the surface resistance to welding of the CuCr25 contact material, facilitating contact breakage and extending contact life.

[0022] Further, in step S4, the sintering process adopts a gradient heating and holding method, which is as follows: heat at room temperature for 1.9 to 2.1 hours, reach 295 to 305°C and hold for 1 to 3 hours; then continue heating for 2.9 to 3.1 hours, reach 495 to 505°C and hold for 1 to 3 hours; heat again for 2 to 5 hours, reach 700 to 1050°C and hold for 1 to 3 hours, and then stop heating;

[0023] Note: By using a gradient heating method, the mixing effect of the consumable electrode rod can be improved, resulting in a more uniform composition of the sintered green body, thereby improving the contact performance of CuCr25.

[0024] Furthermore, in step S5, the parameters for arc melting are: melting current 2000A~3000A, melting voltage 10V~40V, and the number of short circuits during the melting process must be ≤3.

[0025] Note: The above-mentioned arc melting parameters ensure optimal arc melting. Arc melting current exceeding the above range will cause molten pool splashing and increase the possibility of metal burn-off. Current less than 2000A will result in poor arc melting effect. Arc melting voltage should be kept within the above range for optimal performance. Voltage greater than 40V will easily make the molten pool unstable and increase the possibility of metal splashing. Voltage less than 10V will result in poor melting effect. The number of short circuits in arc melting should be kept below three for more uniform component mixing. More than three short circuits will easily cause electrode burn-off.

[0026] Furthermore, in step S5, the environmental temperature and humidity requirements inside the vacuum self-consuming arc melting furnace are: temperature ≤30℃, humidity ≤60%RH;

[0027] Note: The above parameters are designed to minimize the impact of the environment on arc melting, effectively ensuring the performance of CuCr contacts.

[0028] Furthermore, in step S5, the protective gas is argon or helium;

[0029] Explanation: The purpose of introducing gas is twofold: first, to ensure the stability of the electric arc, and second, to prevent excessive evaporation and loss of the furnace charge.

[0030] Furthermore, the mixture is pretreated before the cold isostatic pressing in step S3. The pretreatment method is as follows:

[0031] 1) Take the mixture for later use, and sieve it using a vibrating screen with an aperture of 20-50 μm to obtain 10-50 kg of sieved mixture; prepare the auxiliary adhesive according to the weight-volume ratio of the sieved mixture to the auxiliary adhesive of 10-15 kg: 1 L; divide the sieved mixture and the auxiliary adhesive into several portions.

[0032] 2) Irradiate each portion of the sieved mixture for 10-30 minutes, and then transfer the treated mixture from top to bottom into the rubber sleeve. Add one portion of auxiliary adhesive to the rubber sleeve for each portion of mixture, and repeat this process until all the sieved mixture is filled.

[0033] 3) Evacuate the air inside the rubber sleeve until the pressure reaches 10. -2 After sealing with the rubber sleeve facing upwards, press the powder in the forward direction 5-10 times, then turn the rubber sleeve downwards and press the powder in the reverse direction 1-3 times to complete the powder pressing.

[0034] Explanation: The above method, by first sieving the mixture and then adding the corresponding auxiliary binder in batches, can effectively improve the distribution of the mixture within the rubber sleeve. Irradiation treatment can cause the mixture to vibrate, thereby promoting further thermal motion of the powder. Evacuating the inside of the rubber sleeve to a certain pressure before compaction can enhance the compaction effect. Performing forward compaction first and then reverse compaction can result in better compaction of the mixture. At the same time, the above compaction method can also prevent the rubber sleeve from shrinking.

[0035] Furthermore, in step 2), the specifications of the rubber sleeve are Φ90-200mm, and the material is an elastic rubber sleeve;

[0036] Note: The rubber sleeve of the above material can make the obtained blank more compact and uniform, thereby effectively reducing the occurrence of cracks and uneven density of the blank caused by the relative movement of powder, and further improving the preparation efficiency of CuCr contacts.

[0037] Furthermore, the irradiation treatment is divided into three stages:

[0038] First stage: Take a portion of the sieved mixture and spread it evenly in the pulse microwave equipment. The microwave irradiation power is 300-350W and the irradiation time is 2-5 minutes.

[0039] Second stage: Add another portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 500-700W, irradiation time 2-5min; then apply infrared irradiation treatment to the mixture, infrared irradiation power 230-270W, irradiation time 5-7min.

[0040] Third stage: Add the last portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 400-600W, irradiation time 2-5min;

[0041] Explanation: The above three-stage irradiation treatment method is adopted because the mixture obtained by microwave irradiation alone is not heated evenly, resulting in poor vibration effect of the mixture. In the second stage, infrared irradiation can further induce powder vibration and generate thermal motion, effectively promoting further compaction of the powder. In addition, infrared light can also cause strong interaction between molecules in the powder, further enhancing the compaction effect of the powder.

[0042] Furthermore, the auxiliary adhesive is selected from one of polyurethane resin, epoxy resin, and acrylic resin;

[0043] Note: The above-mentioned auxiliary adhesives all have high-efficiency bonding effect and good fluidity. They have outstanding performance in terms of strength, elasticity and bonding properties. They can be evenly distributed inside the rubber sleeve during the powder preparation process, so that the bonding effect between the mixture and the auxiliary adhesive is better. At the same time, the above-mentioned auxiliary adhesives all have good stability. When mixed with CuCr mixture, they can make it more compact and uniform, and improve its wear resistance and impact resistance.

[0044] Furthermore, in step S4, the obtained green body is subjected to repressing and refiring. The repressing and refiring process is as follows: the sintered green body is placed into a Φ90mm mold for repressing, the repressing pressure is 500-550MPa, the holding time is 20-25s, and the repressed green body is refired at a temperature of 600-800℃ for a holding time of 1-1.2h.

[0045] Explanation: By repressing and re-firing, the density and structural stability of the contact material can be significantly improved, thereby enhancing its resistance to welding. After repressing, while increasing the density of the product, its internal structure undergoes significant grain fragmentation and lattice distortion under strong pressure, resulting in work hardening of CuCr powder particles. After re-firing, the work hardening is eliminated, and the purpose of grain refinement and structural homogenization is achieved.

[0046] The beneficial effects of this invention are:

[0047] (1) The present invention selects ultrafine chromium powder, which is beneficial to optimizing the volume ratio of copper and chromium powder when preparing copper-chromium electrode rods. That is, after ultrafine chromium powder and coarser copper powder are mixed evenly in a certain proportion, the maximum loose density can be obtained. This is because the large pores between the coarse copper powder particles can be filled by some of the fine chromium powder particles, which is beneficial to the uniformity of the powder mixture and the degassing of the electrode rod during vacuum sintering. This ensures that the electrode rod is more stable during the arc melting process and the chromium phase of the prepared material is more uniformly dispersed.

[0048] (2) The present invention further enhances the distribution of the mixture in the rubber sleeve by screening and adding auxiliary binder in batches. Irradiation treatment can cause the mixture to vibrate, thereby promoting further thermal motion of the powder. Pumping the air inside the rubber sleeve to a certain pressure before compacting the powder can enhance the compaction effect of the powder.

[0049] (3) The present invention achieves further vibration compaction of the mixture by combining infrared radiation and microwave radiation, avoiding the situation where the mixture obtained by microwave irradiation alone is not heated evenly and the vibration effect of the mixture is poor. The addition of infrared irradiation further causes the powder to vibrate and generate thermal motion, effectively promoting further compaction of the powder and further enhancing the compaction effect of the powder. Attached Figure Description

[0050] Figure 1 This is a flowchart of the preparation process of the present invention;

[0051] Figure 2 This is a metallographic image of the CuCr25 contact material prepared according to the present invention at 50x magnification;

[0052] Figure 3 This is a metallographic image of the CuCr25 contact material prepared according to the present invention at 100x magnification. Detailed Implementation

[0053] The present invention will now be described in more detail with reference to specific embodiments, so as to better demonstrate the advantages of the present invention.

[0054] Example 1

[0055] A method for preparing CuCr25 contact material using ultrafine powder includes the following steps:

[0056] S1. Raw Material Selection

[0057] Weigh out high-purity, low-gas ultrafine Cr powder with a purity of 99.7% and a particle size of 20–50 μm from aluminothermic reduction, and electrolytic Cu powder with a purity of 99.9% and a particle size of 50–80 μm from Cu powder, according to a Cr powder:Cu powder mass ratio of 25%:75%, and set aside for later use.

[0058] S2, Powder Mixing

[0059] Electrolytic Cu powder and ultrafine Cr powder are mixed and then put into a mixer. Then, stainless steel balls with a size of φ4-12mm are added at a ball-to-powder ratio of 1:1. The stirring speed is adjusted to 25r / min and the mixing time is 4h to obtain the mixture.

[0060] S3, Cold Isostatic Pressing

[0061] The mixture is pretreated before the cold isostatic pressing in step S3. The pretreatment method is as follows:

[0062] 1) Take the mixture for later use, and sieve it using a vibrating screen with a aperture of 35μm to obtain 30kg of sieved mixture; prepare the auxiliary adhesive according to the weight-volume ratio of the sieved mixture to the auxiliary adhesive of 12kg:1L; divide the sieved mixture and the auxiliary adhesive into several equal portions; the auxiliary adhesive is polyurethane resin.

[0063] 2) Irradiate each portion of the sieved mixture for 20 minutes, and then transfer the treated mixture from top to bottom into the rubber sleeve. Add one portion of auxiliary adhesive to the rubber sleeve for each portion of mixture, and repeat this process until all the sieved mixture is filled. The rubber sleeve has a specification of Φ150mm.

[0064] The irradiation treatment is divided into three stages:

[0065] First stage: Take a portion of the sieved mixture and spread it evenly in the pulsed microwave equipment. The microwave irradiation power is 325W and the irradiation time is 4min.

[0066] Second stage: Add another portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 600W, irradiation time 4min; then apply infrared irradiation treatment to the mixture, infrared irradiation power 250W, irradiation time 6min.

[0067] Third stage: Add the last portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 500W, irradiation time 2-5min;

[0068] 3) Evacuate the air inside the rubber sleeve until the pressure reaches 10. -2 After sealing with the rubber sleeve facing upward, press the powder 8 times in the forward direction, then press the powder 2 times in the reverse direction with the rubber sleeve facing downward to complete the powder pressing.

[0069] The rubber sleeve containing the mixture is placed in a cold isostatic press and pressed at a pressure of 250 MPa and a holding time of 8 minutes to obtain a consumable electrode rod.

[0070] S4, Vacuum Sintering

[0071] The consumable electrode rod was transferred to a vacuum of 1×10⁻⁶. -1 The blank is sintered in a vacuum sintering furnace of Pa, with the sintering temperature controlled at about 870℃ and the holding time being 2 hours. Then it is cooled to below 60℃ in the furnace to obtain the blank.

[0072] In step S4, the sintering process adopts a gradient heating and holding method, which is as follows: heat at room temperature for 2 hours, reach 300°C and hold for 2 hours; then continue heating for 3 hours, reach 500°C and hold for 2 hours; heat again for 3.5 hours, reach 870°C and hold for 2 hours, and then stop heating.

[0073] S5, electric arc melting

[0074] The sintered billet is used as a consumable electrode and transferred into a vacuum consumable arc furnace for melting. During the melting process, a protective gas is introduced. After the melting is completed, the molten liquid is poured into a water-cooled copper mold and solidified to obtain an ingot.

[0075] In step S5, the parameters for arc melting are: melting current 2500A, melting voltage 25V, and the number of short circuits during the melting process is 2; the environmental temperature and humidity requirements inside the vacuum self-consuming arc melting furnace are: temperature ≤30℃, humidity ≤60%RH; the protective gas is argon.

[0076] S6, Performance Testing

[0077] After the ingot is melted, it is cooled to 50-60°C, and then the outer diameter is rough-turned, the riser and the bottom plate are sawn to remove casting defects such as shrinkage cavities. Samples are then taken for physical and chemical property testing.

[0078] Example 2

[0079] Unlike Example 1, in step S1, high-purity, low-gas ultrafine Cr powder with a purity of 99.5% and a particle size of 20-50 μm and electrolytic Cu powder with a purity of 99.9% and a particle size of 50-80 μm are weighed out according to the mass ratio of Cr powder to Cu powder of 23% to 77%, and set aside for later use.

[0080] Example 3

[0081] Unlike Example 1, in step S1, high-purity, low-gas ultrafine Cr powder with a purity of 99.9% and a particle size of 20-50 μm and electrolytic Cu powder with a purity of 99.9% and a particle size of 50-80 μm are weighed out according to the mass ratio of Cr powder to Cu powder of 27% to 73%, and set aside for later use.

[0082] Example 4

[0083] Unlike Example 1, in step S2, the stirring speed is adjusted to 10 r / min and the mixing time is 6 h.

[0084] Example 5

[0085] Unlike Example 1, in step S2, the stirring speed is adjusted to 40 r / min and the mixing time is 2 h.

[0086] Example 6

[0087] Unlike Example 1, in the pretreatment method, 1) take the mixture for later use, and use a vibrating screen with a aperture of 20μm to sieve it to obtain 10kg of sieved mixture; prepare the auxiliary adhesive according to the weight-volume ratio of the sieved mixture to the auxiliary adhesive of 10kg:1L.

[0088] Example 7

[0089] Unlike Example 1, in the pretreatment method, 1) take the mixture for later use, and use a vibrating screen with a aperture of 50μm to sieve it to obtain 50kg of sieved mixture; prepare the auxiliary adhesive according to the weight-volume ratio of the sieved mixture to the auxiliary adhesive of 15kg:1L.

[0090] Example 8

[0091] Unlike Example 1, in the pretreatment method, epoxy resin is selected as the auxiliary adhesive.

[0092] Example 9

[0093] Unlike Example 1, in the pretreatment method, acrylic resin is used as the auxiliary adhesive.

[0094] Example 10

[0095] Unlike Example 1, in step 2), the irradiation treatment is divided into three stages:

[0096] First stage: Take a portion of the sieved mixture and spread it evenly in the pulse microwave equipment. The microwave irradiation power is 300W and the irradiation time is 5min.

[0097] Second stage: Add another portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 500W, irradiation time 5min; then apply infrared irradiation treatment to the mixture, infrared irradiation power 230W, irradiation time 7min.

[0098] Third stage: Add the last portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 400W, irradiation time 5min.

[0099] Example 11

[0100] Unlike Example 1, in step 2), the irradiation treatment is divided into three stages:

[0101] First stage: Take a portion of the sieved mixture and spread it evenly in the pulse microwave equipment. The microwave irradiation power is 350W and the irradiation time is 2min.

[0102] Second stage: Add another portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 700W, irradiation time 2min; then apply infrared irradiation treatment to the mixture, infrared irradiation power 270W, irradiation time 5min.

[0103] Third stage: Add the last portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 600W, irradiation time is 2min.

[0104] Example 12

[0105] Unlike Example 1, in step 3), the rubber sleeve is facing upwards and the powder is pounded 5 times in the forward direction. Then, the rubber sleeve is facing downwards and the powder is pounded 1 time in the reverse direction to complete the pounding process.

[0106] Example 13

[0107] Unlike Example 1, in step 3), the rubber sleeve head is facing upwards, and the powder is pounded 10 times in the forward direction. Then, the rubber sleeve head is facing downwards, and the powder is pounded 3 times in the reverse direction to complete the powder pounding.

[0108] Example 14

[0109] Unlike Example 1, in step S4, a gradient heating and holding method is adopted during the sintering process. The gradient heating and holding method is as follows: heat up at room temperature for 1.9h, reach 295℃ and hold for 3h; then continue to heat up for 2.9h, reach 495℃ and hold for 3h; heat up again for 2h, reach 700℃ and hold for 3h, and then stop heating.

[0110] Example 15

[0111] Unlike Example 1, in step S4, a gradient heating and holding method is adopted during the sintering process. The gradient heating and holding method is as follows: heat up at room temperature for 2.1 hours, reach 305°C and hold for 1 hour; then continue to heat up for 3.1 hours, reach 505°C and hold for 1 hour; heat up again for 5 hours, reach 1050°C and hold for 1 hour, and then stop heating.

[0112] Example 16

[0113] Unlike Example 1, in step S4, the obtained green body is subjected to repressing and refiring. The repressing and refiring process is as follows: the sintered green body is placed in a Φ90mm mold for repressing, the repressing pressure is 500MPa, the holding time is 25s, and the repressed green body is refired at a temperature of 600℃ and a holding time of 1.2h.

[0114] Example 17

[0115] Unlike Example 1, in step S4, the obtained green body is subjected to repressing and refiring. The repressing and refiring process is as follows: the sintered green body is placed into a Φ90mm mold for repressing, the repressing pressure is 525MPa, the holding time is 22s, and the repressed green body is refired at a temperature of 700℃ and a holding time of 1.1h.

[0116] Example 18

[0117] Unlike Example 1, in step S4, the obtained green body is subjected to repressing and refiring. The repressing and refiring process is as follows: the sintered green body is placed in a Φ90mm mold for repressing, the repressing pressure is 550MPa, the holding time is 20, and the repressed green body is refired at a temperature of 800℃ for a holding time of 1h.

[0118] Example 19

[0119] Unlike Example 17, in step S5, the parameters for arc melting are: melting current 2000A, melting voltage 10V, and the number of short circuits during the melting process is 1.

[0120] Example 20

[0121] Unlike Example 17, in step S5, the parameters for arc melting are: melting current 3000A, melting voltage 40V, and the number of short circuits during the melting process is 3.

[0122] Experimental Example

[0123] Five samples of CuCr25 contacts prepared in Examples 1-20 and Comparative Examples 1-4 were taken from each example to test the performance of the CuCr contacts. The average value of the performance measurement results of the five samples in each example was taken as the performance measurement result of that example. The specific investigation is as follows:

[0124] 1. Investigate the effects of chromium powder and copper powder particle size on the performance of CuCr25 contacts.

[0125] Table 1. Performance parameters of CuCr25 contacts prepared in Examples 1-3 and Comparative Example 1.

[0126]

[0127]

[0128] Comparative Example 1: Unlike Example 1, high-purity low-gas Cr powder with a purity of 99.7% and a particle size of 70-100 μm and electrolytic Cu powder with a purity of 99.9% and a particle size of 50-80 μm were weighed according to the mass ratio of Cr powder to Cu powder of 25%:75% for later use.

[0129] Conclusion: As shown in Table 1, for CuCr25 material, selecting ultrafine chromium powder is beneficial for optimizing the volume ratio of copper and chromium powder during the preparation of copper-chromium electrode rods. Specifically, mixing ultrafine chromium powder and coarser copper powder in a certain proportion yields the maximum loose density. This is because the large pores between the coarse copper particles can be partially filled by the fine chromium particles, which improves the uniformity of the powder mixture and facilitates degassing of the electrode rod during vacuum sintering. This ensures greater stability of the electrode rod during arc melting, resulting in a more uniform and dispersed chromium phase in the prepared material. In contrast, in Comparative Example 1, the density of the Cr powder exceeded the preferred range proposed in this scheme, leading to a decrease in the loose density of the mixed copper and chromium powder, poor mixing uniformity, and reduced material stability.

[0130] 2. Investigate the effects of pretreatment and pretreatment processes on the performance of CuCr25 contacts.

[0131] Table 2. Performance parameters of CuCr25 contacts prepared in Examples 1, 6-11 and Comparative Examples 2-4

[0132]

[0133]

[0134] Comparative Example 2: Unlike Example 1, no pretreatment is performed on the mixture. The mixture is directly loaded into the rubber sleeve and crushed 8 times in the forward direction. Then, with the rubber sleeve head facing down, it is crushed 2 times in the reverse direction to complete the crushing. The rubber sleeve containing the mixture is then placed into a cold isostatic press and pressed at a pressure of 250 MPa and a holding time of 8 minutes to obtain the consumable electrode rod.

[0135] Comparative Example 3: Unlike Example 1, the auxiliary adhesive used is a hot melt adhesive.

[0136] Comparative Example 4: Unlike Example 1, the irradiation treatment was performed using microwave irradiation.

[0137] Conclusion: Comparing the data of Example 1 and Control Example 2 in Table 2, the lack of pretreatment of the mixture leads to a significant decrease in the performance of CuCr25. This is because the powder compaction process can only achieve preliminary compaction of the powder, and its effect on the density and uniformity of the mixture is still unsatisfactory. The method proposed in this invention, which involves adding the mixture in batches with the auxiliary binder and then performing air extraction on the rubber sleeve, can further improve the density and uniformity of the mixture and enhance the performance parameters of the CuCr25 contact. The comparison of the data of Example 1 and Examples 6-7 shows that the weight-volume ratio of the mixture to the auxiliary binder has little impact on the performance of the finished CuCr25 contact.

[0138] Comparison of data from Examples 1, 8-9 and Comparative Example 3 shows that replacing the auxiliary adhesive with hot melt adhesive has little impact on the performance of the CuCr25 contact product. However, since hot melt adhesive itself has anti-peel properties and does not significantly improve the hardness of the contact, Example 1 is the optimal solution to avoid damage during the subsequent demolding process.

[0139] A comparison of the data from Examples 1, 10-11 and Comparative Example 4 shows that the mixture obtained by microwave irradiation in Comparative Example 4 was not heated evenly, resulting in poor vibration effect of the mixture and thus reducing the performance of the CuCr contact. In this method, the addition of infrared irradiation in the second stage can further induce the vibration of the powder and generate thermal motion, effectively promoting further compaction of the powder. In addition, infrared light can also cause strong interaction between the molecules in the powder, further enhancing the compaction effect of the powder.

[0140] 3. Investigate the effect of the re-pressing and re-firing process on the performance of CuCr25 contacts.

[0141] Table 3 Performance parameters of CuCr25 contacts prepared in Examples 1, 16-18

[0142] Group Hardness (HB) Electrical conductivity (MS / m) <![CDATA[Density (g / cm 3 )]]> Example 1 209 27.5 8.35 Example 16 211 27.9 8.37 Example 17 215 28.3 8.91 Example 18 213 28.1 8.52

[0143] Conclusion: The comparison of data from Examples 1 and 16-18 in Table 3 shows that the re-pressing and re-firing process has a significant promoting effect on the performance parameters of CuCr25 contacts. This is because after re-pressing, while increasing the density of the product, its internal structure undergoes significant grain fragmentation and lattice distortion under strong pressure, resulting in work hardening of CuCr powder particles. After re-firing, the work hardening is eliminated, and the purpose of grain refinement and structural homogenization is achieved. Therefore, considering all factors, Example 17 is the optimal solution.

Claims

1. A method for preparing CuCr25 contact material using ultrafine powder, characterized in that, Includes the following steps: S1. Raw Material Selection Weigh out high-purity, low-gas ultrafine Cr powder with a purity of 99.5% to 99.9% and a particle size of 20 to 50 μm from aluminothermic reduction, and electrolytic Cu powder with a purity of 99.9% and a particle size of 50 to 80 μm from Cu powder, according to the mass ratio of Cr powder to Cu powder of 23% to 27% to 73% to 77%, and set aside for later use. S2, Powder Mixing Electrolytic Cu powder and ultrafine Cr powder are mixed and then fed into a mixer, with a ball-to-powder ratio of 1:

1. Use 4-12mm stainless steel pebbles, adjust the stirring speed to 10-40 r / min, and mix for 2-6 hours to obtain a mixture; S3, Cold Isostatic Pressing The mixture is pretreated, and the pretreatment method is as follows: 1) Take the mixture for later use, and sieve it using a vibrating screen with an aperture of 20~50μm to obtain 10~50kg of sieved mixture; prepare the auxiliary adhesive according to the weight-volume ratio of the sieved mixture to the auxiliary adhesive of 10~15kg:1L; divide the sieved mixture and the auxiliary adhesive into several portions. 2) Irradiate each portion of the sieved mixture for 10-30 minutes, and then transfer the treated mixture from top to bottom into the rubber sleeve. Add one portion of auxiliary adhesive to the rubber sleeve for each portion of mixture, and repeat this process until all the sieved mixture is filled. The irradiation treatment is divided into three stages: First stage: Take a portion of the sieved mixture and spread it evenly in the pulse microwave equipment. The microwave irradiation power is 300~350W and the irradiation time is 2~5min. Second stage: Add another portion of the sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 500~700W, irradiation time 2~5min; then apply infrared irradiation treatment to the mixture, infrared irradiation power 230~270W, irradiation time 5~7min. Third stage: Add the last sieved mixture to the pulse microwave oven, use the adjusting plate to spread the mixture evenly in the pulse microwave oven, microwave irradiation power 400~600W, irradiation time 2~5min; 3) Evacuate the air inside the rubber sleeve until the pressure reaches 10. -2 After sealing with the rubber sleeve facing upward, press the powder in the forward direction 5-10 times, then turn the rubber sleeve downward and press the powder in the reverse direction 1-3 times to complete the powder pressing. The rubber sleeve containing the mixture is placed into a cold isostatic press and pressed at a pressure of 150~350MPa and a holding time of 5~10min to obtain the consumable electrode rod. S4, Vacuum Sintering The consumable electrode rod was transferred to a vacuum of 1×10⁻⁶. -1 The blank is sintered in a vacuum sintering furnace of Pa, with the sintering temperature controlled between 700 and 1050°C and the holding time between 1 and 3 hours. Then it is cooled to below 60°C in the furnace to obtain the blank. S5, electric arc melting The sintered billet is used as a consumable electrode and transferred into a vacuum consumable arc furnace for melting. During the melting process, a protective gas is introduced. After the melting is completed, the molten liquid is poured into a water-cooled copper mold and solidified to obtain an ingot. S6, Performance Testing After the ingot is melted, it is cooled to 50~60℃, and then the outer diameter is rough turned, the riser and the bottom plate are sawn to remove shrinkage casting defects, and samples are taken for physical and chemical property testing.

2. The method for preparing CuCr25 contact material using ultrafine powder according to claim 1, characterized in that, In step S4, the sintering process adopts a gradient heating and holding method, which is as follows: heat at room temperature for 1.9~2.1h, reach 295~305℃ and hold for 1~3h; then continue heating for 2.9~3.1h, reach 495~505℃ and hold for 1~3h; heat again for 2~5h, reach 700~1050℃ and hold for 1~3h, and then stop heating.

3. The method for preparing CuCr25 contact material using ultrafine powder according to claim 1, characterized in that, In step S5, the parameters for arc melting are: melting current 2000A~3000A, melting voltage 10V~40V, and the number of short circuits during the melting process must be ≤3.

4. The method for preparing CuCr25 contact material using ultrafine powder according to claim 1, characterized in that, In step S5, the environmental temperature and humidity requirements inside the vacuum self-consuming arc melting furnace are: temperature ≤30℃, humidity ≤60%RH.

5. The method for preparing CuCr25 contact material using ultrafine powder according to claim 1, characterized in that, In step S5, the protective gas is argon or helium.

6. The method for preparing CuCr25 contact material using ultrafine powder according to claim 1, characterized in that, In step 2), the specifications of the rubber sleeve are Φ90-200mm.

7. The method for preparing CuCr25 contact material using ultrafine powder according to claim 1, characterized in that, The auxiliary adhesive is selected from one of polyurethane resin, epoxy resin, and acrylic resin.

Images